1. Field of the Invention
This invention pertains to the field of polyurethanes. More particularly, this invention relates to the preparation and use of fire-retardant polyurethanes such as polyurethane foams which are made utilizing 2,4,5-tribromoimidazole as a fire-retardant chemical.
2. Description of the Prior Art
It has become increasingly important to impart flame-resistance properties to polyurethane plastics. This is particularly true where cellular polyurethanes are used, for example, as insulation to prevent the risk of fire in the daily use of many items. Numerous methods are known for imparting fire-resistant properties to polyurethane plastics. For example, in the production of the cellular polyurethanes, one may use halogenated compounds or derivatives of acid phosphorus as the active hydrogen-containing component and thus impart flame-resistance. It is also possible to use compounds containing antimony or boron.
While many halogen-containing compounds such as bromine-containing additives have been proposed as chemicals to promote fire-retardance, in many instances such proposed materials are deficient in one or more respects. For example, use of such fire-retardant chemicals sometimes materially adversely affects the properties of the resultant polyurethane, and particularly polyurethane foam. Thus, for example, use of such additives may in many instances adversely affect compressive and tensile strengths, lead to poor (high) K factors, and undesirable low percentage of closed cells, deleteriously affect dimensional stability, etc. Still other bromine-containing fire-retardant additives do not have a sufficiently high bromine content whereby an unduly large amount of the additive must be used to achieve the desired effectiveness. This is a particularly penalizing drawback if the additive is non-functional, that is, does not react with the isocyanate. In still further instances, the halogenated compound does not have a sufficiently high stability at conventional use temperatures, does not properly decompose on burning, has an insufficiently low volatility, etc.
It would, therefore, be a substantial advance in the art if use of a fire-retardant chemical for polyurethane compositions could be discovered which does not materially affect the final properties of the polyurethane composition, and yet imparts a sufficiently adequate fire-retardance property to the polyurethane.